The present invention relates to a method and apparatus for creating a beam of electromagnetic radiation that raster scans over a two-dimensional area.
The advantages of inspecting an object or a person with penetrating radiation, where the radiation is formed into a beam of specified cross-section and is scanned sequentially over a portion or the entirety of the object or person, are well known. Applications of a scanned x-ray beam, for example, include, but are not limited to, medical diagnostics and surveillance to detect concealed contraband materials at border crossings or sensitive sites.
A source of penetrating radiation typically emits a cone of radiation that may be formed, by means of collimators, into a fan beam that is narrower in one dimension and broader in a perpendicular dimension. In the prior art, if the beam to be scanned is a pencil beam, the fan beam emitted by the source is typically blocked by an attenuating material other than at an aperture of specified area where a beam is emitted that is scanned along one dimension, as described., for example, in U.S. Pat. No. Re 28,544 (Stein et al., reissued Sep. 2, 1975). In order to illuminate the entirety of a region, either the inspected object is translated with respect to the source (as baggage is typically moved on a conveyor belt for inspection), or else the source and scanning arrangement are translated with respect to the inspected object, as is known in the art of inspecting large objects such as cargo containers.
In accordance with one aspect of the invention, in one of its embodiments, there is provided a device for scanning a beam in two dimensions as a periodic function of time. The device has a wheel having an axis of rotational symmetry, the wheel being opaque to a specified energy range of electromagnetic radiation. The wheel has a set of apertures for transmitting the radiation in such a manner that the radiation is emitted in a beam from each of a specified number of apertures at a time. The device also has two rotary actuators. The first rotary actuator is coupled to the wheel for rotating the wheel about the axis of rotational symmetry of the wheel such that the beam is scanned in a plane perpendicular to the axis of rotational symmetry of the wheel. The second rotary actuator rotates the wheel about an axis not parallel to the axis of rotational symmetry.
In accordance with alternate embodiments of the invention, the specified number of apertures emitting a beam at any one time may be one. The device may also have a source of penetrating radiation for emitting radiation incident upon an inner surface of the wheel.